UV laser micromachining of piezoelectric ceramic using a pulsed Nd:YAG laser

UV laser (=355 nm) ablation of piezoelectric lead zirconate titanate (PZT) ceramics in air has been investigated under different laser parameters. It has been found that there is a critical pulse number (N=750). When the pulse number is smaller than the critical value, the ablation rate decreases with increasing pulse number. Beyond the critical value, the ablation rate becomes constant. The ablation rate and concentrations of O, Zr and Ti on the ablated surface increase with the laser fluence, while the Pb concentration decreases due to the selective evaporation of PbO. The loss of the Pb results in the formation of a metastable pyrochlore phase. ZrO₂ was detected by XPS in the ablated zone. Also, the concentrations of the pyrochlore phase and ZrO₂ increase with increasing laser fluence. These results clearly indicate that the chemical composition and phase structure in the ablated zone strongly depend on the laser fluence. The piezoelectric properties of the cut PZT ceramic samples completely disappear due to the loss of the Pb and the existence of the pyrochlore phase. After these samples were annealed at 1150 °C for 1 h in a PbO-controlled atmosphere, their phase structure and piezoelectric properties were recovered again. Finally, 1–3 and concentric-ring 2–2 PZT/epoxy composites were fabricated by UV laser micromachining and their thickness modes were measured by impedance spectrum analysis and a d₃₃ meter. Both composites show high piezoelectric properties. PACS 81.40.Gh; 77.84.-s     

Experimental study of electro-optical-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd:YAG laser. We experimentally study and compare the performance of the pulsed Nd:YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configuration of the optical resonator. In this laser, an unsymmetrical concave–concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 m J with an FWHM pulse width of 7 ns at100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.     

Enhanced drilling using a dual-pulse Nd:YAG laser

A new method for improving the efficiency of laser drilling has been developed. Two synchronized free-running laser pulses from a tandem-head Nd:YAG laser are capable of drilling through 1/8-in-thick stainless-steel targets at a stand-off distance of 1 m without gas-assist. The combination of a high-energy laser pulse for melting with a properly tailored high-intensity laser pulse for liquid expulsion results in the efficient drilling of metal targets. We argue that the improvement in drilling is due to the recoil pressure generated by rapid evaporation of the molten material by the second laser pulse. Received: 29 August 2000 / Accepted: 18 December 2000 / Published online: 3 April 2001     

Experimental study of electro-optical Q-switched pulsed Nd:YAG laser

We report the specification of a compact and stable side diode-pumped Q-switched pulsed Nd:YAG laser. We experimentally study and compare the performance of the pulsed Nd:YAG laser in the free-running and Q-switched modes at different pulse repetition rates from 1 Hz to 100 Hz. The laser output energy is stabilized by using a special configuration of the optical resonator. In this laser, an unsymmetrical concave-concave resonator is used and this structure helps the mode volume to be nearly fixed when the pulse repetition rate is increased. According to the experimental results in the Q-switched operation, the laser output energy is nearly constant around 70 mJ with an FWHM pulse width of 7 ns at 100 Hz. The optical-to-optical conversion efficiency in the Q-switched regime is 17.5%.     

Biocompatible film deposition by using Nd:YAG pulsed laser

A Nd:YAG laser operating at the fundamental wavelength (1064 nm) and at the second harmonic (532 nm), with 9 ns pulse duration, 100–900 mJ pulse energy, and 30 Hz repetition rate mode, was employed to ablate in vacuum (10^?6 mbar) biomaterial targets and to deposit thin films on substrate backings. Titanium target was ablated at the fundamental frequency and deposited on near-Si substrates. The ablation yield increases with the laser fluence and at 40 J/cm ² the ablation yield for titanium is 1.2×10¹⁶ atoms/pulse. Thin film of titanium was deposited on silicon substrates placed at different distance and angles with respect to the target and analysed with different surface techniques (optical microscopy, scanning electron spectrosopy (SEM), and surface profile).

Hydroxyapatite (HA) target was ablated to the second harmonic and thin films were deposited on Ti and Si substrates. The ablation yield at a laser fluence of 10 J/cm ² is about 5×10¹⁴ HA molecules/pulse. Thin film of HA, deposited on silicon substrates placed at different distance and angles with respect to the target, was analysed with different surface techniques (optical microscopy, SEM, and Raman spectroscopy).

Metallic films show high uniformity and absence of grains, whereas the bio-ceramic film shows a large grain size distribution. Both films found special application in the field of biomaterial coverage.     

Femtosecond laser drilling of alumina ceramic substrates

In the paper, the result on femtosecond laser drilling of alumina ceramic substrate was reported. The effects of various laser parameters such as different focus position, traverse speed, drilling pattern, pausing time, etc. on the drilled hole quality in terms of surface finish, heat affected zone (HAZ), hole circularity, debris, microcracks were studied. The quality of laser-drilled holes on alumina ceramic substrates was evaluated with optical microscope, SEM/EDX, and X-ray μ-CT analysis. The optimum drilling conditions were identified. High-quality laser-drilled holes on alumina ceramic substrates were demonstrated. The developed process has potential application in manufacturing of alumina substrate based electronic devices.     

Laser welding of glasses using a nanosecond pulsed Nd:YAG laser

This work reports on laser welding of two 1 mm thickness borosilicate glasses through the irradiation with a nanosecond pulsed laser, as a novel alternative to the use of ultrashort pulsed lasers for welding of transparent materials. Two different methodologies were investigated and compared in terms of interface quality. In a first approach, the glasses were joined without any absorbing intermediate layer. However, the bond interface possesses defects. To improve the resulting bond interface, the use of a titanium ultrathin intermediate layer was proposed to weld the glasses substrates, acting as a sealant between them. The laser parameters were optimized to achieve the best joining conditions of the Ti film. The use of the Ti layer gives rise to a bond interface more homogeneous and free of damages. As a further step, thin glasses of 86 µm thickness, of great technological value, were joined through the Ti film as well. The joined interfaces were inspected through optical microscopy and scanning electron microscopy (SEM) while the bond quality was evaluated by Scanning Acoustic Microscopy (SAM).     

Multi-performance characterization analysis of diameter and taper angle on alumina ceramic via using pulsed ultraviolet laser percussion drilling method

This paper presents the optimal conditions for the ultraviolet laser percussion drilling of alumina materials intended for use in heat sinks. The Taguchi method and grey relational analysis, along with the consideration of multiple quality characteristics, were applied for determining the optimal parameters. The entrance diameter and taper angle of the drilled hole were affected by the material processing parameters, including laser power, pulse duration, focal plane position, and number of pulses. The Taguchi method and grey relational analysis were used for assessing the effects of the operational parameters on multiple performance characteristics. Nine experiments based on an orthogonal array were performed. According to the results, the optimal process parameters were as follows: laser energy density, 3.82 J/cm²; focal plane position, 0.1 mm; number of pulses, 20 shots; and single pulse duration, 3 ms. Analysis of the grey relational grade revealed that the focal plane position was the most dominant parameter.     

Stable seeder-injected Nd:YAG pulsed laser using a RbTiOPO_4 phase modulator

A stable, single-longitudinal-mode, nanosecond-pulsed Nd:YAG laser with a laser-diode dual-end pumping arrangement is constructed. Injection seeding is performed successfully by utilizing a Rb Ti OPO4 crystal as the intracavity phase modulator to change the optical length of the slave cavity based on the delay-ramp-fire technique. The laser generates 9.9 m J of pulse energy with a 16 ns pulse duration at a 400 Hz repetition rate.A near-diffraction-limit laser beam is achieved with a beam quality factor M2 of approximately 1.2. The frequency jitter is 1.5 MHz over 2 min, and the fluctuation of the output pulse power is 0.3% over 23 min.     

Side-pumped continuous-wave Cr:Nd:YAG ceramic solar laser

To clarify the advantages of Cr:Nd:YAG ceramics rods in solar-pumped lasers, a fused silica light guide with rectangular cross-section is coupled to a compound V-shaped cavity within which a 7 mm diameter 0.1 at.% Cr:1.0 at.% Nd:YAG ceramic rod is uniformly pumped. The highly concentrated solar radiation at the focal spot of a 2 m diameter stationary parabolic mirror is transformed into a uniform pump radiation by the light guide. Efficient pump light absorption is achieved by pumping uniformly the ceramic rod within the V-shaped cavity. Optimum pumping parameters and solar laser output powers are found through ZEMAX^© non-sequential ray-tracing and LASCAD^© laser cavity analysis codes. 33.6 W continuous-wave laser power is measured, corresponding to 1.32 times enhancement over our previous results with a 4 mm diameter Nd:YAG single-crystal rod. High slope efficiency of 2.6 % is also registered. The solar laser output performances of both the ceramic and the single-crystal rods are finally compared, revealing the relative advantage of the Cr:Nd:YAG rod in conversion efficiency. Low scattering coefficient of 0.0018 cm^?1 is deduced for the ceramic rod. Heat load is considered as a key factor affecting the ceramic laser output performance.     

钛宝石激光器端面抽运Nd:YAG陶瓷激光器热沉积理论和实验研究

通过热沉积系数研究在激光提取条件下掺杂原子分数为1.0%的Nd:YAG陶瓷激光器中热沉积问题.热沉积系数定义为热沉积功率与激光器输出功率之比.在理论分析基础上，通过测量激光器斜率效率来间接测定热沉积系数，实验测定的热沉积系数值为0.63.建立激光提取条件下Nd:YAG陶瓷发热模型，讨论了影响热沉积系数的主要因素.结果表明：热沉积系数对Nd:YAG陶瓷的辐射量子效率、交叠效率以及激光提取效率的变化非常敏感.为有效减少介质内热沉积，在激光器优化设计中交叠效率和激光提取效率是需要着重考虑的参数.所得结果可为进一步研究陶瓷激光器中热效应提供参考. 关键词： 热沉积 Nd:YAG陶瓷 固体激光器     

Quality of the beam produced a pulsed Nd:YAG laser

The quality of the beam produced by a Nd:YAG laser was investigated. A hemispherical Nd:YAG laser resonator was developed. A flashlamp driver was designed to pump a Nd:YAG laser crystal. The output of the laser was characterized via the variation of the capacitor voltage. A phosphor card was used to detect the invisible of the infrared beam. Exposed photographic paper was utilized to examine the energetic beam after interaction. The brightness and strength of the beams were analyzed using the Matrox Inspector and VideoTest 5 software packages. The intensity of the beam produced and the volume loss after interaction were found to linearly increase with respect to the input energy.     

Hollow-fiber delivery of high-power pulsed Nd:YAG laser light

We propose hollow fibers for delivery of high-peak-power pulsed Nd:YAG laser light. Hollow fibers with an internal polymer layer were fabricated by a liquid-phase coating technique. We reduced the losses of the fibers in the near-infrared region by producing a silver film that was very smooth owing to use of an ultrasonic wave for mixing of the silver and the reducer solutions in the silver-plating process. The straight losses of the 1-m-long polymer-coated fibers were 0.3 dB for the 700-mum bore size and 0.1 dB for the 1000-mum bore fiber.     

高功率高光束质量脉冲Nd: YAG激光器

 以实现高功率、高光束质量的脉冲激光输出为目的,对非对称平-凹谐振腔的结构进行了理论分析。设计出了高功率、高光束质量非对称放置的平-凹谐振腔、双氙灯泵浦的脉冲Nd: YAG激光器。当占空比为9%时,实现输出激光平均功率近480 W,光束参数积优于12.7 mm·mrad,电光转化效率近4%,与理论分析吻合,可用芯径300 μm的光纤传输,不稳定性优于±1%。加工实验证明有较好的质量：切割材料为不锈钢,厚度为3 mm时、切割速度为0.6 m/min和厚度为1.5 mm、切割速度为1.2 m/min时,两种情况下所得切缝宽度均为250 μm,且切割上下沿光滑。     

Investigation of Cr:YAG passive mode-locking in a pulsed Nd:YAG laser

Passive mode-locking of a pulsed Nd:YAG laser using a Cr⁴⁺:YAG saturable absorber was realized for the first time in a nearly critical stable resonator containing an antiresonant ring structure. The output energy and pulse duration are 13.5 mJ and 180 ps, respectively. The recovery time and saturable intensity for excited-state absorption of Cr⁴⁺:YAG under the action of strong laser pulses were calculated from rate equations.     

高功率高光束质量脉冲Nd: YAG激光器

以实现高功率、高光束质量的脉冲激光输出为目的,对非对称平-凹谐振腔的结构进行了理论分析。设计出了高功率、高光束质量非对称放置的平-凹谐振腔、双氙灯泵浦的脉冲Nd: YAG激光器。当占空比为9%时,实现输出激光平均功率近480 W,光束参数积优于12.7 mm·mrad,电光转化效率近4%,与理论分析吻合,可用芯径300 μm的光纤传输,不稳定性优于±1%。加工实验证明有较好的质量：切割材料为不锈钢,厚度为3 mm时、切割速度为0.6 m/min和厚度为1.5 mm、切割速度为1.2 m/min时,两种情况下所得切缝宽度均为250 μm,且切割上下沿光滑。     

A kilowatt level diode-side-pumped QCW Nd:YAG ceramic laser

We demonstrate a kilowatt level Quasi-continuous-wave (QCW) diode-side-pumped Nd:YAG ceramic laser at 1064 nm. The laser system adopts a master oscillator power amplifier scheme (MOPA). The master oscillator contains two diode-pumped laser modules. Under the pump power of 2000 W, an output power of 686 W was obtained. After amplified by an identical ceramic laser module, a maximum output power of 1020 W was obtained under a total incident pump power of 3433 W, corresponding to an optical-optical conversion efficiency of 29.7%. At the maximal output power, the repetition frequency was measured to be 1 kHz and the pulse width was 114 μs. To the best of our knowledge, this is the first time to realize QCW side-pumped Nd:YAG ceramic laser system with output power above 1 kW.     

Liquid-cooled ceramic Nd:YAG split-disk amplifier for high-average-power laser

A liquid-cooled ceramic Nd:YAG split-disk laser amplifier has been designed for a high-average-power laser system. The maximum average output power of 17.1 W (1.71 J at 10 Hz) and the beam size of far-field pattern with 1.5 times diffraction limit was obtained. The combination of liquid cooling for disk laser material and wavefront compensation with a phase conjugation mirror was demonstrated. The wavefront degradation by liquid cooling was observed and measured with Michelson interferometer and far-field patterns.     

LD抽运的Nd:YAG陶瓷/KTP绿光激光器

报道了一种LD端面抽运Nd:YAG陶瓷、KTP腔内倍频的全固态连续波绿光激光器.当抽运功率为21.6 W时,1064 nm基频输出达到11.3 W,光—光转换效率为52.3%.采用Ⅱ类切割的KTP晶体作为腔内倍频介质,在直腔结构下获得了最大功率为1.86 W的532　nm绿光输出,光—光转换效率为7%.输出光斑具有高斯型强度分布,1 W输出时的M²因子约为1.7. 关键词： 全固态绿光激光器 Nd:YAG陶瓷 KTP倍频 直腔